A mass spectrometer is an apparatus for detecting the molecular structure of a test sample by selecting molecular ions formed by an ionization source and measuring the mass of the fragment ions with a mass analyzer, wherein the ionization source ionizes the test sample using electrospray ionization (ESI) and matrix assists laser desorption ionization (MALDI) methods, and the mass analyzer includes an ion trap analyzer, time-of-flight analyzer, quadrupole analyzer and Fourier transform ion cyclotron resonance (FT-ICR) analyzer.
A tandem mass spectrometer uses a combination of one or more different types of the various mass analyzers, and is classified into a tandem mass spectrometer using a tandem-in-space mass analysis method and a tandem mass spectrometer using a tandem-in-time mass analysis method.
The tandem mass spectrometer using the tandem-in-space mass analysis method generally uses the quadrupole analyzer and the ion trap analyzer. One of two mass analyzers spaced apart from each other selects and separates ions that will be measured, and then transmits the separated ions to a collision cell having a collision gas. The other of the two separate mass analyzers measures the mass of fragment ions transmitted from the collision cell, wherein the fragment ions are generated by colliding the separated ions with the collision gas.
The tandem mass spectrometer using the tandem-in-time mass analysis method uses a trap type mass analyzer such as a FT-ICR analyzer, and performs an ion selection process and a mass measurement process with a time interval in the same mass analyzer.
The tandem mass spectrometer using the tandem-in-space mass analysis method generally has a low resolution in selecting the ions with a specific mass, thus having a limitation in selecting and separating the ions of the specific mass with high resolution. The resolution is calculated by dividing the width at half height of a peak in a mass spectrum by the value of m/z (mass-to-charge ratio) at the peak.
The tandem mass spectrometer using the tandem-in-time mass analysis method can select the ions with a specific mass at high resolution in a FT-ICR trap using a FT-ICR analyzer. In this case, an inert collision gas is injected into the FT-ICR trap for generating fragment ions, the fragment ions are generated by colliding the inert collision gas with the ions selected by the FT-ICR mass analyzer, and the masses of the generated fragment ions are measured in the FT-ICR trap.
However, in the tandem mass spectrometer using the tandem-in-time mass analysis method, the radius of ion cyclotron motion is reduced because the peripheral pressure in the FT-ICR trap is increased by injecting the inert collision gas. Accordingly, the magnitude of ion detection signal is gradually decreased and the resolution and the magnitude of a mass spectrum are reduced.
Also, the peripheral gas in the FT-ICR trap must be removed after generating the fragment ions and thus the mass of the fragment ions cannot be measured quickly.